The major aim of this project is to examine the mechanism by which cholesterogenesis is articulated with DNA replication. Previous studies supported by this grant have demonstrated that mevalonic acid is required for the synthesis of DNA, specifically during the S phase of the cell cycle. We have further shown that the isoprenoid purine, isopentenyl adenine, is approximately 100 times more effective in regulating DNA replication than mevalonic acid itself. During the coming year we shall study the biochemical pathway of isopentenyl adenine synthesis in animal tissues. The various classes of DNA polymerase will be isolated from normal and malignant tissues of varying growth rates. We will then determine whether the inhibition of mevalonic acid synthesis inhibits the activity of these polymerases, and if so, whether mevalonic acid and isopentenyl adenine can restore polymerase activity. By this approach, we hope to determine the mechanism by which isopentenyl adenine or related isoprene derivatives regulate DNA replication and thereby the rate of cell replication in normal and cancerous cells.